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Abstract:

Provided are a multilayer ceramic capacitor and a manufacturing method
thereof, which can stably secure capacitance and prevent cracking caused
by the diffusion of an electrode material. The multilayer ceramic
capacitor includes a capacitor body where an inner electrode including a
first electrode material and a dielectric layer are alternately
laminated, and an outer electrode disposed on an outer surface of the
capacitor body and electrically connected to the inner electrode, the
outer electrode including a second electrode material. A diffusion layer
having a length exceeding 1 μm in which the first and second electrode
materials are mixed is provided at a region where the inner electrode and
the outer electrode are connected to each other.

Claims:

1. A multilayer ceramic capacitor comprising: a capacitor body where an
inner electrode including a first electrode material and a dielectric
layer are alternately laminated; and an outer electrode disposed on an
outer surface of the capacitor body and electrically connected to the
inner electrode, the outer electrode including a second electrode
material, wherein a diffusion layer having a length exceeding 1 μm in
which the first and second electrode materials are mixed is provided at a
region where the inner electrode and the outer electrode are connected to
each other.

2. The multilayer ceramic capacitor of claim 1, wherein the diffusion
layer has a length less than 13 μm.

6. The multilayer ceramic capacitor of claim 1, wherein the number of
laminated dielectric layers is in a range of 50 to 1,000.

7. A method of manufacturing a multilayer ceramic capacitor, the method
comprising: forming a capacitor body by laminating an inner electrode
including a first electrode material and a dielectric layer alternately;
forming an outer electrode electrically connected to the inner electrode
on an outer surface of the capacitor body, the outer electrode including
a second electrode material; forming a passivation layer including a
dielectric forming material on at least one of top and bottom surfaces of
the capacitor body; compressing the capacitor body; and firing the
capacitor body, wherein a diffusion layer having a length exceeding 1
μm in which the first and second electrode materials are mixed is
formed at a region where the inner electrode and the outer electrode are
connected to each other.

8. The method of claim 7, wherein the diffusion layer is formed to have a
length less than 13 μm.

9. The method of claim 7, wherein the first electrode material is
comprised of Ni or Ni alloy.

10. The method of claim 7, wherein the second electrode material is
comprised of Cu or Cu alloy.

11. The method of claim 7, wherein the diffusion layer is comprised of
Ni/Cu alloy.

12. The method of claim 7, further comprising cutting the capacitor body
to form respective units, between the compressing of the capacitor body
and the firing of the capacitor body.

13. The method of claim 7, wherein the number of laminated dielectric
layers is in a range of 50 to 1,000.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of Korean Patent Application
No. 10-2009-0129305 filed on Dec. 22, 2009, in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein by
reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a multilayer ceramic capacitor and
a manufacturing method thereof, and more particularly, to a multilayer
ceramic capacitor capable of not only stably securing capacitance but
also preventing cracking caused by the diffusion of an electrode
material, and a manufacturing method thereof.

[0004] 2. Description of the Related Art

[0005] In general, multilayer ceramic capacitors include a plurality of
ceramic dielectric sheets and inner electrodes interposed between the
ceramic dielectric sheets. Multilayer ceramic capacitors are being widely
used as capacitive parts in various electronic devices, due to their
small size, high capacity and ease of mounting.

[0006] Recently, as electronic products have become compact and
multi-functional, chip components have also tended to become compact and
highly functional. Following this trend, multilayer ceramic capacitors
are required to be smaller but to have a higher capacitance than ever
before. Accordingly, multilayer ceramic capacitors where a dielectric
layer has a thickness of 2 μm or less and number of laminated layers
is 500 or more have recently been manufactured.

[0007] An outer electrode is installed at a lateral cross section where an
inner electrode is exposed among lateral cross sections of a ceramic
capacitor. Generally, a typical conductive paste used for forming an
outer electrode contains a copper powder into which a glass frit, a base
resin, an organic vehicle, and the like are mixed.

[0008] The outer electrode is formed by coating a lateral cross section of
a ceramic capacitor with an outer electrode paste, and firing the ceramic
capacitor coated with the outer electrode paste to sinter metal powders
in the outer electrode paste.

[0009] In the case of a multilayer ceramic capacitor with small number of
laminated layers, cracking caused by a diffusion phenomenon from an outer
electrode to an inner electrode does not occur even though a diffusion
layer is sufficiently formed between the outer electrode and the inner
electrode. Therefore, a major concern is focused on a technique of
reducing capacitance deviation by increasing the contact property
maximally, as one of several key techniques in polishing, outer electrode
paste preparation, and outer electrode firing.

[0010] However, in the case of a multilayer ceramic supercapacitor with a
large number of laminated layers, although the contact property between
the outer electrode and the inner electrode is increased, there is a
serious problem which does not take place in the multilayer ceramic
capacitor with small number of laminated layers. Specifically, when the
diffusion occurs heavily from the outer electrode toward the inner
electrode in the multilayer ceramic capacitor with large number of
laminated layers, cracking is generated due to the expansion in the
volume of the inner electrode, resulting in a decrease in bending
strength, and moreover, a plating solution penetrates into the generated
cracks to thereby degrade the reliability of a product.

SUMMARY OF THE INVENTION

[0011] An aspect of the present invention provides a multilayer ceramic
capacitor that can not only stably secure capacitance but also prevent
cracking caused by the diffusion of an electrode material, and a
manufacturing method thereof.

[0012] According to an aspect of the present invention, there is provided
a multilayer ceramic capacitor including: a capacitor body where an inner
electrode including a first electrode material and a dielectric layer are
alternately laminated; and an outer electrode disposed on an outer
surface of the capacitor body and electrically connected to the inner
electrode, the outer electrode including a second electrode material,
wherein a diffusion layer having a length exceeding 1 μm in which the
first and second electrode materials are mixed is provided at a region
where the inner electrode and the outer electrode are connected to each
other.

[0013] The diffusion layer may have a length less than 13 μm.

[0014] The first electrode material may include nickel (Ni) or Ni alloy.

[0015] The second electrode material may include copper (Cu) or Cu alloy.

[0016] The diffusion layer may include Ni/Cu alloy.

[0017] The number of laminated dielectric layers may be in a range of 50
to 1,000.

[0018] According to another aspect of the present invention, there is
provided a method of manufacturing a multilayer ceramic capacitor,
including: forming a capacitor body by laminating an inner electrode
including a first electrode material and a dielectric layer alternately;
forming an outer electrode electrically connected to the inner electrode
on an outer surface of the capacitor body, the outer electrode including
a second electrode material; forming a passivation layer including a
dielectric forming material on at least one of top and bottom surfaces of
the capacitor body; compressing the capacitor body; and firing the
capacitor body, wherein a diffusion layer having a length exceeding 1
μm in which the first and second electrode materials are mixed is
formed at a region where the inner electrode and the outer electrode are
connected to each other.

[0019] The diffusion layer may be formed to have a length less than 13
μl.

[0020] The first electrode material may be comprised of Ni or Ni alloy.

[0021] The second electrode material may be comprised of Cu or Cu alloy.

[0022] The diffusion layer may be comprised of Ni/Cu alloy.

[0023] The method may further include cutting the capacitor body to form
respective units, between the compressing of the capacitor body and the
firing of the capacitor body.

[0024] The number of laminated dielectric layers may be in a range of 50
to 1,000.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and other aspects, features and other advantages of the
present invention will be more clearly understood from the following
detailed description taken in conjunction with the accompanying drawings,
in which:

[0026]FIG. 1 is a perspective view of a multilayer ceramic capacitor
according to an embodiment of the present invention;

[0027]FIG. 2 is a cross-sectional view taken along line A-A' of FIG. 1;

[0028]FIG. 3 is a cross-sectional view taken along line B-B' of FIG. 1;
and

[0029] FIGS. 4A to 4C are cross-sectional views illustrating a
manufacturing process of a multilayer ceramic capacitor according to an
embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] Hereinafter, exemplary embodiments of the present invention will be
described with reference to the accompanying drawings to fully explain
the present invention in such a manner that it may easily be carried out
by a person with ordinary skill in the art to which the present invention
pertains. In the detailed description of exemplary embodiments of the
present invention below, detailed descriptions related to well-known
functions or configurations will be left out in order not to
unnecessarily obscure subject matters of the present invention.

[0031] Throughout the drawings, like reference numerals denote like
elements having the same construction and function.

[0032] In this disclosure below, when one part is referred to as being
`connected` to another part, it should be understood that the former can
be `directly connected` to the latter, or `electrically connected` to the
latter via an intervening part.

[0033] Furthermore, when it is described that one comprises (or includes
or has) some elements, it should be understood that it may comprise (or
include or has) only those elements, or it may comprise (or include or
have) other elements as well as those elements if there is no specific
limitation.

[0034] Herebelow, a multilayer ceramic capacitor and a manufacturing
method thereof according to an embodiment of the present invention will
be described with reference to FIGS. 1 to 4.

[0035]FIG. 1 is a perspective view schematically illustrating a
multilayer ceramic capacitor according to an embodiment of the present
invention, FIG. 2 is a cross-sectional view taken along line A-A' of FIG.
1, FIG. 3 is a cross-sectional view taken along line B-B' of FIG. 1, and
FIGS. 4A to 4C are cross-sectional views schematically illustrating a
manufacturing process of a multilayer ceramic capacitor according to an
embodiment of the present invention.

[0036] A multilayer ceramic capacitor according to the embodiment of the
present invention may include a capacitor body 1 and outer electrodes 2.

[0037] In the capacitor body 1, a plurality of dielectric layers 6 are
laminated, and inner electrodes 4 are inserted between the dielectric
layers 6. The dielectric layers 6 may be formed of barium titanate
(Ba2TiO3).

[0038] The inner electrodes 4 may be formed of a first electrode material
including nickel (Ni) or a Ni alloy. The outer electrodes 2, which are
formed at both sides of an outer surface of the capacitor body 1 and
electrically connected to the inner electrodes 4, are formed of a second
electrode material including copper (Cu) or a Cu alloy. The outer
electrodes 2 may serve as external terminals because they are formed to
be electrically connected to the inner electrodes 4 exposed to the outer
surface of the capacitor body 1.

[0039] Here, a diffusion layer 4a having a length exceeding 1 μm in
which the first and second electrode materials are mixed is formed in a
region where the inner electrode 4 and the outer electrode 2 are
connected to each other. Also, the diffusion layer 4a is formed to have a
length less than 13 μl. The diffusion layer 4a includes the second
electrode material diffused from the outer electrode 2, and is thus
comprised of Ni/Cu alloy.

[0040] The multilayer ceramic capacitor according to the embodiment of the
present invention may include an effective layer 20 provided with the
dielectric layers 6 and the inner electrodes 4 that are alternately
laminated. Also, the multilayer ceramic capacitor may include a
passivation layer 10 obtained by laminating dielectric layers on top and
bottom surfaces of the effective layer 20.

[0041] Since the passivation layer is formed by sequentially laminating
plural dielectric layers on the top and bottom surfaces of the effective
layer 20, the effective layer 20 may be protected from external impacts
or the like.

[0042] When the inner electrode 4 of the effective layer 20 is formed of
Ni, the inner electrode 4 has a thermal expansion coefficient of about
13×10-6/, whereas the dielectric layer 6 formed of ceramic has
a thermal expansion coefficient of about 8×10-6/. When a
thermal shock is applied during a firing process and a mounting process
of a circuit board by a reflow solder, a stress is exerted on the
dielectric layer 6 due to a difference in thermal expansion coefficient
between the dielectric layer 6 and the inner electrode 4. Accordingly,
cracking may be generated in the dielectric layer 6 because of the stress
caused by thermal shock.

[0043] Even when the diffusion occurs heavily from the outer electrode 2
toward the inner electrode 4, cracking may also be generated due to the
expansion in the volume of the inner electrode 4. This causes a plating
solution to penetrate into the generated cracks, leading to a decrease in
product reliability.

[0044] Therefore, to not only stably secure capacitance but to also
prevent the generation of cracking caused by the thermal shock and the
expansion in the volume of the inner electrode 4, a manufacturing process
is controlled in such a manner that the diffusion layer 4a obtained by
the diffusion of the second electrode material into the inner electrode 4
should have a length greater than 1 μm but less than 13 μm after
being fired, thereby improving the contact property between the inner
electrode 4 and the outer electrode 2. Here, the diffusion layer 4a is
formed on at least one of both ends of the inner electrode 4, and an
appropriate length of the diffusion layer 4a of the inner electrode 4 may
be determined through experimentations.

EMBODIMENT

[0045] As illustrated in FIG. 4A, dielectric layers 6 of a capacitor body
1 were formed to include a binder, a plasticizer and a balance of
dielectric material. Conductive inner electrodes 4 containing Ni were
printed on the dielectric layers 6 obtained by molding a slurry having
the above-described composition. Thereafter, a multilayer body with a
predetermined thickness was made out of the printed dielectric layers 6.
Here, number of the laminated dielectric layers 6 was in the range of 50
to 1,000.

[0046] Afterwards, as illustrated in FIG. 4B, the resultant is compressed
at a predetermined temperature. Herein, it was exemplified that the
multilayer ceramic capacitor had a W-section with a large cumulative
stepped amount because empty spaces between the inner electrodes 4
printed in parallel and the dielectric layers 6 were alternately
laminated. In an L-section of the multilayer ceramic capacitor, the
dielectric layer 6 is also laminated in the empty space between the inner
electrodes 4 printed in parallel like the W-section. However, the
L-section of the multilayer ceramic capacitor differs from the W-section
in that the empty space between the inner electrodes 4 is not positioned
over the dielectric layer 6 but the inner electrode 4 is printed on the
dielectric layer 6. Therefore, the W-section has a cumulative stepped
amount that is relatively larger than that of the L-section, and thus the
dielectric layer 6 between the inner electrodes 4 printed in parallel is
further recessed during compression.

[0047] Thereafter, as illustrated in FIG. 4c, respective multilayer
ceramic capacitors were formed by cutting the recessed portion of the
multilayer ceramic capacitor.

[0049] Table 1 shows test results for a capacitance of each multilayer
ceramic capacitor, cracking caused by thermal shock and diffusion, and
reliability according to a depth of the diffusion layer 4a of the inner
electrode 4 in each of the multilayer ceramic capacitors that are
prepared according to different firing conditions after coating an end of
an outer surface of the capacitor body 1 with the second electrode
material, e.g., copper paste.

[0050] From Table 1, even in case where the depth of the diffusion layer
4a is 1 μm or less, there is no problem in cracking and reliability
that may be caused by the expansion in the volume of the inner electrode
4, however, there is a problem of a decrease in capacitance due to poor
contact property. It can be understood that a capacitance is in a normal
range but cracking is generated due to the expansion in the volume of the
inner layer 4 if the depth of the diffusion layer 4 is 13 μm or more.
Furthermore, it can be understood that a capacitance is in a normal range
but number of cracks and reliability problems caused by the expansion in
the volume of the inner layer 4 are significantly increased if the depth
of the diffusion layer 4 is 16 μm or more. According to these results,
it can be seen that it is possible to realize a multilayer ceramic
supercapacitor with large number of laminated layers by controlling the
diffusion layer 4a of the inner electrode 4 to have a depth greater than
1 μm but smaller than 13 μm.

[0051] As set forth above, according to exemplary embodiments of the
invention, it is possible to provide a multilayer ceramic capacitor and a
manufacturing method thereof, which cannot only stably secure capacitance
but also prevent cracking caused by the diffusion of an electrode
material.

[0052] Also, a crack and delamination due to the diffusion from an outer
electrode to an inner electrode can be prevented by improving the contact
property at an interface between the inner electrode and the outer
electrode.

[0053] In addition, by establishing relations among a capacitance, the
generation of cracks and a reliability problem according to the depth of
the diffusion layer from the outer electrode to the inner electrode and
the reliability of the multilayer ceramic supercapacitor having large
number of laminated layers can be enhanced through appropriately
controlling of the depth of the diffusion layer.

[0054] While the present invention has been shown and described in
connection with the exemplary embodiments, it will be apparent to those
skilled in the art that modifications and variations can be made without
departing from the spirit and scope of the invention as defined by the
appended claims.

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